The present invention relates a semiconductor device in which a plurality of resistors having the same characteristics are formed on an element isolation layer at a high accuracy while suppressing variations of the respective characteristics.
In a conventional semiconductor device, as shown in FIG. 17, the surface of a silicon substrate 1 is selectively oxidized to obtain a field oxide film 3a serving as a dioxide silicon layer. This region has been used as a region for element isolation.
However, with micropatterning of elements in recent years, an element isolation layer called an STI (Shallow Trench Isolation) which can be designed to be accurate has been used. The outline of a method of manufacturing the STI is shown in FIG. 18A to FIG. 18F.
As shown in FIG. 18A to FIG. 18F, a protective film 2 is stacked on a silicon substrate 1 shown in FIG. 18A (FIG. 18B). The protective film 2 is selectively etched to obtain a structure in FIG. 18C. Etching is performed by using the protective film 2 as a mask to form a trench in the silicon substrate 1 as shown in FIG. 18D. Subsequently, a silicon oxide film 3 is deposited by plasma CVD or the like to obtain a structure shown in FIG. 18E. Finally, the resultant structure is subjected to a polishing process such as CMP (Chemical Mechanical Polish) to obtain a structure shown in FIG. 18F.
Even though an element isolation region obtained by the field oxide film 3a is an isolation region having a wide area as shown in FIG. 17, a structure in which the thickness of the central portion and the thickness of the peripheral portion are almost equal to each other is difficult to obtain because of the nature of the manufacturing method. In contrast to this, since the element isolation layer region obtained by the STI is subjected to the polishing process such as the CMP, a relatively wide area (e.g., 10 xcexcmxc3x9710 xcexcm or more) has a characteristic structure in which the central portion is thinner than, i.e., dented relative to, the peripheral portion.
However, in such an element isolation region obtained by the STI, a new problem which is not posed in a conventional field oxide film has been posed. More specifically, when a plurality of resistors having the same characteristics are to be formed on an element isolation layer region having a relatively wide area, as shown in FIG. 19A and FIG. 19B, focus is offset by the positions of the resistors in a photolithographic operation because of the dent described above. Therefore, the resistors vary in size, and it is difficult to form a plurality of resistors having the same characteristics with a high accuracy.
It is an object of the present invention to provide a semiconductor device in which a plurality of resistors having the same characteristics are formed at a high accuracy on an element isolation layer region formed by a polishing process such as STI.
According to the semiconductor device of one aspect of the present invention, a plurality of resistors having the same characteristics are formed on an element isolation layer, at least one diffusion region exists between one resistor and a resistor adjacent thereto, and the plurality of resistors and the diffusion regions are arranged such that all distances between the respective resistors and the diffusion regions around the corresponding resistors are equal to each other.
According to the semiconductor device of another aspect of the present invention, a plurality of resistors having the same characteristics are formed on an element isolation layer, at least one metal wiring layer exists between one resistor and a resistor adjacent thereto, and the plurality of resistors and the metal wiring layers are arranged such that all distances between the resistors and the metal wiring layers around the corresponding resistors are equal to each other.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.